Image-guided therapy (IGT), which is also often referred to as image-guided intervention (IGI), has gained widespread attention and clinical acceptance for use in localizing tumors in abdominal organs. Procedures that utilize IGT include, but are not limited to, tumor biopsy and ablation.
IGT essentially describes the interactive use of medical images during a percutaneous procedure, and is often referred to as a “global positioning system” (GPS) for interventional radiology. For example, in an automobile GPS, the current position of a vehicle is accurately localized or “registered” onto an electronic roadmap located on the dashboard. As the automobile moves, its position is updated on this roadmap. The driver can use the GPS as a guide to see where their vehicle is, where it has been and where it is headed, and can follow a planned route to a selected destination. IGT allows the physician to accomplish the same thing with their tracked medical instruments on the 3-D “roadmap” of highly detailed tomographic medical images of the patient that are ideally acquired and studied well before the interventional procedure. The key step in an IGT procedure is the accurate registration between real “patient” space and medical image space.
In an ideal IGT procedure, a 3D map or plan is created from the preoperative diagnostic images, possibly days before the actual procedure and in consultation with a variety of physicians in different disciplines. On the day of the percutaneous procedure, the position of the patient and the medical instruments are accurately localized or “registered” onto these preoperative images in the interventional suite. As the physician moves the instrument, the precise location of its tip is updated on the 3-D images. The physician can then quickly follow a planned path to a selected destination (for example, a tumor or other lesion of interest). The exact location of the instrument is confirmed with a form of real-time imaging, including, but not limited to, intraoperative computerized tomography (CT), 2-D fluoroscopy, or ultrasonic (US) imaging.
U.S. Pat. No. 7,853,307, “Methods, Apparatuses, And Systems Useful In Conducting Image Guided Interventions,” which is incorporated herein in its entirety by specific reference for all purposes, discloses a method to register the pre-operative images to patient space using non-tissue reference markers/skin fiducial markers. This invention uses radio opaque fiducial markers (also known as skin fiducial markers) attached to the patient's abdomen, and a full CT scan of the patient's abdomen immediately before the procedure (also known as intra-procedural images), and performs a point-based registration to achieve correspondence between the fiducial markers' location on the abdomen and its corresponding position in the intra-procedural CT images. Similarly, U.S. Pat. No. 6,785,571, “Device and Method for Registering A Position Sensor In An Anatomical Body,” which is incorporated herein in its entirety by specific reference for all purposes, discloses a method to register pre-operative images to patient space using a tracked instruments inserted into the patient's body.
Both these prior arts suffers from the disadvantage that the highly detailed diagnostic images cannot be easily used during the interventional procedure. This means that the physicians do not have access to detailed visualizations of lesions and vasculature, and also do not have the time to create an ideal procedure plan. The existing technology also requires that the patients be scanned at least twice (once for pre-procedural diagnostic images and a second time for the intra-procedural images), which increases their exposure to X-ray radiations. Therefore, it would be ideal to use the high quality diagnostic CT or MR medical images directly for percutaneous guidance by performing a registration using those images. Point-based registration techniques discussed in the prior art are not accurate and inaccurate registrations compromise the accuracy of guidance during interventional procedures.
U.S. Patent App. No. 60/859,439, “Apparatus And Methods For Compensating For Organ Deformation, Registration Of Internal Structures To Images, And Applications Of The Same,” which is incorporated herein in its entirety by specific reference for all purposes, details a method to perform registrations using pre-operative diagnostic images. The registration method disclosed in the patent uses surfaces generated from pre-operative diagnostic images and surfaces obtained during surgical or interventional procedures and “salient anatomical features” (anatomical regions that can be easily identified on both the surfaces) and performs a rigid surface-based registration to align the surfaces obtained during surgical or interventional procedures to the pre-operative surfaces. However, the method relies on the assumption that “salient anatomical features” can be easily identified on both sets of surfaces. Further, “salient anatomical features” cannot be obtained during percutaneous procedures. Therefore, there is a need to perform registration using something other than skin markers and salient anatomical features.
Surface registration using salient anatomical features in image-guided surgery is described more fully in Clements, et al, “Robust surface registration using salient anatomical features in image-guided liver surgery,” Medical Imaging 2006: Visualization, Image-guided Procedures, and Display: Proc. of the SPIE (2006), and Clements, et al, “Robust surface registration using salient anatomical features for image-guided liver surgery: Algorithm and validation,” Medical Physics, Vol. 35, No. 6, pp. 2528-2540 (2008); copies of the above are appended to U.S. Provisional Application No. 61/331,252, all of which are incorporated herein in their entireties by specific reference for all purposes.